<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <title>Document</title>
  <style>
    .ceshi {
      font-size: 14px;
    }

    .a {
      font-size: 2em;
    }

    .ganga {
      font-size: 2rem
    }

    .transion {
      width: 100px;
      height: 100px;
      transition: width 2s;
      background: red;
    }

    .transion:hover {
      width: 200px;
    }
  </style>
</head>

<body>
  <div class="transion">

  </div>
  <div class="ceshi">
    <p class="a">测试一下</p>
    <div>号发偶滴神</div>
  </div>
  <div>
    <p class="ganga">发尴尬了</p>
  </div>
</body>

</html>